The long term aim is to combine basic and applied research so as of modern psychophysical and neurophysiological vision research to advancing our knowledge of human eye and brain disorders, to improving diagnostic and monitoring procedures, and to improving tests for comparing experimental therapies. To achieve our short term aims we will further develop our motion-defined letter reading test for detecting visual loss hidden to Snellen acuity and contrast sensitivity tests and, by comparing motion- defined letter test results with the results of other visual tests in patients with known brain lesions, we will establish the specificity of the test. Our short term aims are as follows: (1) Find whether focal lesions in parietal cortex can produce selective loss of the ability to detect and/or read motion-defined letters while sparing sensitivity to local or to global motion, color vision, fine depth perception, and the ability to read contrast-defined letters of high and low contrast (i.e. visual acuity for high- and low- contrast letters). Find whether focal lesions in temporal cortex produce patterns of loss in which the ability to detect and read motion-defined letters is spared. (2) Find whether multiple sclerosis can cause the patterns of loss described in (1). (3) By investigating the effects of dot lifetime and stimulus presentation duration, determine the extent to which the losses of ability to detect and/or read motion-defined letters in (1) and (2) are a consequence of abnormal dynamics of motion processing.